Field of Invention
The present invention relates to a turbocharger for a combustion engine, and a method of operating such a turbocharger. More specifically, the invention relates to a turbocharger, and a method of operating a turbocharger, which has a variable turbine geometry.
Description of Related Art
Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing, thereby driving a radial air compressor that is mounted onto a common shaft with the turbine. A turbocharged engine can be more powerful and efficient than a naturally aspirated engine because the turbine forces more air, and proportionately more fuel, into the combustion chamber than atmospheric pressure alone.
To achieve efficient and powerful operation of the engine under different load and speed conditions, so-called variable-geometry turbochargers (VGTs) allow the amount of exhaust gas that is passed through the turbine housing to be regulated by varying the turbine geometry, typically by selectively opening or closing an exhaust gas channel or passage to the turbine. For example, the position of a flow-restricting member is controlled by a pneumatic or electric actuator to a position that depends on the operating point of the engine.
Conventionally, such control does not take into account pressure pulsations in the exhaust gas channel, which originate from the operation of the cylinders and valves of the combustion engine, but is based on average pressure values over one or more engine cycles. That means, the flow-restricting member is set to a compromise position that is optimal for the highest and lowest pressure values occurring in the pulsations. In order to recover more of the energy present in the pulsating exhaust gas stream, WO 2006/061588 A1 suggests a flow control device for a turbocharger, which includes a sensor for sensing a measure of turbo charger inlet pressure, and a controller arranged to control the position of the flow restrictor based on sensed pressure in the turbocharger inlet.
However, due to the rapid pressure changes in the exhaust gas pressure pulsations, controlling the position of the flow restrictor based on sensed pressure places high demands on the time resolution and processing power of the controller employed in the control device, furthermore leading to high electrical power consumption. It therefore is desirable to reduce the amount of processing power required while recovering a high proportion of the energy present in the pulsating exhaust gas stream.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.